Vena cava filter

ABSTRACT

A vena cava filter and placement set includes features which can be visualized utilizing sonography. A method of implanting a vena cava filter employs sonography to enable the surgeon to direct the filter to a desired location and ensure that the filter is properly deployed. Designs include members of wire and slotted tubes, constructed of temperature-sensitive shape memory materials and of mechanically expanded materials.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/408,467, filed Sep. 28, 1999, now U.S. Pat. No. 6,080,178,which is incorporated herein by reference and which is related toprovisional U.S. patent applications Ser. Nos. 60/129,955 and60/134,664, filed Apr. 20, 1999 and May 18, 1999, respectively, bothincorporated herein in their entirety by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to implantable blood filters.More particularly, the invention relates to caval filters havingsonographically conspicuous features.

2. Related Art

Advances in many surgical specialties have saved the lives of manypatients suffering serious illness or injury, and have improved thequality of life of countless others. However, such surgical repair oforgans and tissues can disrupt the body's plumbing, e.g., thecirculatory system, sufficiently to give rise to new risks. For thisreason, minimally invasive techniques have been developed, for examplewherein highly specialized surgical tools are manipulated from outside apatient's body through a catheter or tube inserted through a tinyincision or puncture and guided to a surgical site. Yet, both invasiveand minimally invasive procedures disturb circulation sufficiently sothat arterial plaques can become dislodged or clots can form in thebloodstream and move with the circulation with the body. Such debris,moving along with normal circulation, can become lodged in and partiallyor completely block vessels supplying blood and oxygen to criticalorgans, such as the heart, lungs and brain.

Medication is often used to reduce the likelihood of blood clotformation during and after surgery, however, post-operative thrombosis,as such blood clot formation is called, remains an important problem tobe solved. Therefore, filters implantable in a patient's body usingminimally invasive techniques have been developed. By appropriatelypositioning such filters, dangerous blood clots can be removed fromcirculation and held in a safe location until they can be dissolved bymedication or extracted, again using minimally invasive techniques.Thus, there has been a significant reduction in the incidence ofmorbidity and mortality due to post-operative embolism, which occurswhen a thrombolus moves from its site of formation to block a vessel,becoming an embolus.

Conventional implantable blood filters employing a variety of geometriesare known. Many are generally basket or cone shaped, in order to provideadequate clot-trapping area while permitting sufficient blood flow. Alsoknown are filters formed of various loops of wire, including somedesigned to partially deform the vessel wall in which they areimplanted.

Along with their many functional shapes, conventional filters mayinclude other features. For example, peripheral loops or arms may beprovided to perform a centering function so that a filter is accuratelyaxially aligned with the vessel in which it is implanted. In order toprevent migration under the pressure induced by normal circulation, manyfilters have anchoring features. Such anchoring features may includesharp points, ridges, etc. Finally, conventional filters are known whichhave specific features for facilitating implanting and extracting usingcatheterization. Thus, a surgeon can select from a variety ofconventional filters, to optimize one or another parameter of interest,and implant or extract that filter using minimally invasive techniques.

The minimally invasive techniques mentioned above require that a surgeonguide a catheter to a precise location within a patient's body. Theprecise location within the body is visualized using conventional x-rayimaging and marked on the patient's body with marker or using x-rayfluoroscopy during surgery. The position of the catheter or otherinstrument within the body is visualized using similar techniques. As iswell-known, x-rays, a form of ionizing radiation, produce an imageshowing by variations in image density corresponding variations intransmission density indicative of the position of various anatomicalstructures and of the instrument introduced into the body by thesurgeon. In order to improve the fluoroscopic image of soft tissues,such as blood vessels, contrast media are sometimes introduced into avessel to be imaged. An instrument, which might otherwise beradiologically transparent, may also be given a radiopaque tip or otherfeature. However, exposure to ionizing radiation or contrast media iscontraindicated for a significant number of patients, such as pregnantwomen or patients exhibiting anaphylactic reactions to contrast media.

SUMMARY OF THE INVENTION

What is desired is a filter, which is implantable, in vivo in a humanblood vessel, without the problems or disadvantages noted above.

In one embodiment, the invention may be realized in a filter,implantable in a blood vessel by sonographic visualization. Such afilter may include one or more members arranged to trap blood clotswithout substantially interfering with normal blood flow; and anechogenic feature on at least one member, so the filter position can bedetermined by sonographic visualization. In such a filter, the echogenicfeature may, for example, be a bead or a tube. Alternatively, theechogenic feature can simply by a textured or etched surface or a sharpedge or any other feature, surface, coating or geometry which issonographically conspicuous. The filter may be placed with theassistance of a marker wire including a plurality of echogenic markers,whereby correct visualization in a sonogram of a true longitudinal slicealong the filter axis is readily ascertainable by presence in thesonogram of each of the plurality of echogenic markers. Alternatively,the filter may include an echogenic tube through which the marker wireis threaded; correct visualization in a sonogram of a true longitudinalslice along the filter axis is further confirmed by presence in thesonogram of the tube in its entirety.

Filters embodying the invention may be characterized by severaldifferent geometries. For example, in one geometry, one or more membersare arranged to define a cone-shaped basket attached to the echogenicfeature at a vertex. The members may be further arranged to define asubstantially coplanar flower, the echogenic feature attached thereto ata center thereof. The cone and flower geometries may be combined, beingjoined by an outer ring connecting a base of the cone to an outerposition of the flower. The basket may be defined by substantiallyradially extending members or by a mesh of members extending in bothradial directions and directions transverse the radial directions.Visibility using sonography of various geometries using the cone may befurther enhanced by a plurality of echogenic markers substantially at aperiphery of a base of the cone.

Filters embodying the invention may include other enhancements, as well.For example, the filter may include a plurality of loops at a peripheryof the basket, whereby the basket is axially aligned thereby duringdeployment thereof. The filter may also include a plurality of echogenicmarkers substantially at a periphery of the filter, whereby deploymentthereof can be visualized.

Alternative filter geometries can also include an expanded, slotted tubehaving slots along a predetermined length thereof, the slots dividingthe slotted tube into the one or more members. Some of the geometriescan be constructed with members composed of a material having atemperature-sensitive shape memory. In such an embodiment, the filtermay have a deployed shape at human body temperature and a compact shapefor implantation at a temperature other than human body temperature.

According to another aspect of the invention, there is a method ofimplanting a blood filter in a blood vessel, comprising steps of: movinga blood filter having an echogenic feature through the blood vessel toan implantation site in the blood vessel; and during the step of moving,visualizing the echogenic feature of the filter and the implantationsite sonographically. Adjusting a sonographic transducer to correctlyvisualize in a sonogram a true longitudinal slice along the filter axis,which is readily ascertainable, may enhance this method by presence inthe sonogram of at least one echogenic feature of the filter.

According to yet another aspect of the invention, a caval filterplacement set includes a guide wire, a dilator, a sheath for introducingthe filter, a caval filter including one or more members arranged totrap blood clots without substantially interfering with normal bloodflow, and an echogenic feature on the caval filter, so the filterposition can be determined by sonographic visualization. Moreover, theguide wire may be bent to facilitate locating a renal vein.

These and other features, objects and advantages of the invention willbecome apparent upon reading the following detailed description of someembodiments thereof, in connection with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, in which like reference designations indicate likeelements:

FIG. 1 is a side view of one embodiment of a filter according to someaspects of the invention;

FIG. 2 is a top view of the embodiment of FIG. 1;

FIG. 3 is a side view of another embodiment of a filter according toaspects of the invention;

FIG. 4 is a top view of yet another embodiment of a filter according toaspects of the invention;

FIG. 5 is a side view of yet another embodiment of a filter according toaspects of the invention;

FIG. 6 is a top view of the embodiment of FIG. 5;

FIG. 7 is a side view of a modification of a conventional filterembodying aspects of the invention;

FIG. 8 is a side view of one embodiment of a filter according to someaspects of the invention;

FIG. 9 is a top view of the embodiment of FIG. 8;

FIG. 10 is a side view of one embodiment of a filter according to someaspects of the invention;

FIG. 11 is a top view of the embodiment of FIG. 10;

FIG. 12 is a side view of a twisted slotted tube filter embodyingaspects of the invention;

FIG. 13 is a side view of the slotted tube from which the filter of FIG.12 is formed;

FIG. 14 is a side view of a single member of the slotted tube filter ofFIG. 12;

FIG. 15 is a top view of the twisted slotted tube filter of FIG. 12;

FIG. 16 is a side view of a conic slotted tube filter embodying aspectsof the invention;

FIG. 17 is a side view of the slotted tube from which the filter of FIG.16 is formed.

FIG. 18 is a side view of another slotted tube filter embodying aspectsof the invention;

FIG. 19 is a side view of a bent guide or marker wire;

FIGS. 20 and 21 are side views showing placement of the bent guide wirein the vicinity of the renal veins within the vena cava;

FIG. 22 is a side view of an echogenic tube mounted over a guide ormarker wire;

FIG. 23 is a sketch of a true sonographic image of an echogenic tube andguide wire; and

FIG. 24 is a sketch of an oblique sonographic image of an echogenic tubeand guide wire.

DESCRIPTION

The present invention will be better understood upon reading thefollowing description of several embodiments thereof, in connection withthe drawings.

The present invention may be embodied in a set of devices for deliveryof a caval filter to a desired position in a patient's body, preferablyabsent the use of fluoroscopic guidance. A caval filter embodyingaspects of the invention is constructed of nitinol wire, a materialknown to have temperature-sensitive shape memory when suitably preparedas known in the art, in a form which is compact at room ambienttemperature, but which expands to an operating configuration at apatient's body temperature. Alternatively, stainless steel, titanium, orother known materials implantable in the human body can be used.Materials not having temperature-sensitive shape memory can be used inconnection with known mechanical expansion techniques. Also, the filtercan be of a slotted tube design made to expand either mechanically or bymeans of shape memory properties as with nitinol construction. Thefilter includes a sonographically conspicuous feature at a distal,leading end thereof, by which the filter can be guided into position byuse of sonographic imaging. The sonographically conspicuous featurecould be located at another known position on the filter, as well. Asused herein, a sonographically conspicuous feature is one whosesonographic image, density, shape, etc. contrasts significantly with theimage produced by other features. Examples of such sonographicallyconspicuous features include, but are not limited to beads, tubes, flatsurfaces, textured surfaces including etched surfaces, sharp corners,sharp edges highly reflective or absorptive coatings and embedded bodiesof various shapes and materials contrasting with the surroundingmaterial. All of these either substantially increase or decrease thereturn of a sonographic signal relative to surrounding features. Inorder to improve the accuracy of positioning using the sonographicallyconspicuous feature at the distal end of the filter, a preferred filtergeometry and deployment apparatus is defined in such a way as to avoidforeshortening or other movement of the distal end of the filter duringdeployment. However, geometries, which do not avoid such movement, canalso be used. Also, sonographically conspicuous features may be includedon the guide wire by which the filter is inserted and positioned in thepatient's body.

Filters embodying the invention can also include sonographicallyconspicuous features located at the periphery of the filter. Thesefeatures may be located at or near either end of the filter, dependingon the design of the filter. Placing sonographically conspicuousfeatures at the peripheral ends of the filter struts allows the openingof the filter to be observed using sonographic imaging, if so desired.These peripheral, sonographically conspicuous features can mark the endsof filter struts or crossbars, as well as the ends of the filter. Theends of the filter can also be marked separately, as described above.

Filters according to some aspects of the present invention can includeboth sonographically and flouroscopically conspicuous features. Byincorporating both types of features, better use of available facilitiesand equipment, training and other useful purposes may be served.

One type of sonographically conspicuous feature is one that is highlyechogenic. A highly echogenic feature reflects a substantial portion ofthe ultrasound energy directed at it at a frequency of interest. A roughsurface finish, having numerous acoustic interfaces, is more echogenicthan a smoother surface finish. Also, a larger surface is more echogenicthan a smaller one having a similar surface finish. Conventionalbent-wire and slotted tube designs have been found not to besonographically apparent.

Filters according to the principles of the present invention may bepermanently implantable, e.g., having hooks to keep the filter in place,or may be removable, e.g., relying solely on pressure to keep the filterin place. Such filters can also have a variety of shapes suitable fortheir filtering purpose, as is known in the art. One preferred filterhas an inverted cone-shaped basket at the proximal end thereof, forfiltering. Some illustrative embodiments are now described in connectionwith the accompanying Figures.

The side view of FIG. 1 and the top view of FIG. 2 show one filter 101having an echogenic feature located as described above. Three continuousstrands of nitinol wire 103, 105, 107 form the illustrated filter 101.The upper strand 103 is coiled into an upper flower form having fiveloops 111. The lower strand 107 is coiled into a lower cone form, alsohaving five loops 115. Finally, the middle strand 105 is coiled into anouter ring having ten loops, five directed up 109 and five directed down113.

The upper loops 109 of the middle strand 105 join the loops 111 of theupper strand 103; the lower loops 113 of the middle strand 105 join theloops 115 of the lower strand 107. The lower cone formed by the lowerstrand 107 has a vertex 117 joined to the center 119 of the upper flowerformed by the upper strand 103 at weld 121. Weld 121 defines anechogenic bead 123. Preferably weld 121 has a diameter of 2 mm, althoughthe diameter may also be as small as about 1 mm or even as large asabout 3 mm. The diameter should be sufficient to define the echogenicbead 123 so as to provide adequate sonographic conspicuousness.

Filter 101 of this embodiment is preferably about 3 cm long and about 3cm in diameter when fully expanded. In use, the filter may not expandfully, slight compression holding it in place where the surgeon desires.

Various alternative filter design features are now described inconnection with FIGS. 3-7. These figures show various features which canbe combined in numerous other permutations and combinations than shown,as will be apparent to those skilled in this art.

The side view of FIG. 3 shows alternative configurations for anechogenic feature and for centering features. In this alternativeconfiguration, an echogenic tube 301 supports individual wire strands303 arranged as a cone filter. Wire strands 303 further supportindividual centering loops 305. The components are welded or brazedtogether using conventional techniques. Echogenic properties areimparted to the tube 301 by virtue of its size and surface finish, asdescribed above. In preferred configurations using an echogenic tube301, the tube 301 has an inside diameter large enough to freely pass a0.035 inch (0.89 mm) diameter guidewire. Also preferred in someconfigurations, the tube 301 has a flared, dilated or contracted feature307 at one end to facilitate gripping of the tube 301 for purposes ofremoving the filter after it has served its purpose.

Although FIGS. 1-3 show filter wires (e.g., 107, 303) which aregenerally straight or smooth curves, as shown in FIG. 4, bent filterwires 401 can reduce the size of openings between wires, resulting in amore effective filter, without blocking the free flow of normal blood.

FIGS. 5 and 6, side and top views, respectively, illustrate aconfiguration employing an echogenic tube 301, as described above, towhich straight filter wires 501 are conventionally welded or brazed.Instead of centering loops 305, this configuration has a split side ring503 to prevent filter migration, once placed where desired by thesurgeon. Spring pressure pushes the split side ring 503 into the vesselwall when the filter is in the position desired, thus anchoring thefilter against the pressure of blood flow through the filter. Gaps 505between segments of the split side ring 503 allow the filter to becompressed to a smaller diameter than when deployed for insertion,removal or positioning within a vessel of a patient's body. Instead ofstraight filter wires 501, this configuration can use bent filter wires401, as in the configuration of FIG. 4. The echogenic tube 301 can havethe characteristics and features described above in connection with FIG.3, if desired.

A modification of a conventional filter design made by MediTech, BostonScientific (Natick, Mass.) is illustrated in the side view of FIG. 7. Inthis configuration, filter 701 includes an echogenic tube 301 not foundin the conventional MediTech design. The echogenic tube 301 of thisconfiguration also may include the features described above, such as theextraction feature 307.

Yet another filter configuration is shown in FIGS. 8 and 9 in side andtop view, respectively. The filter 800 shown has a central echogenictube 301, supporting a plurality of bent wires 801, 803. Bent wires 801are arranged as one filter cone, while bent wires 803 are arranged as asecond filter cone. Bent wires 801 and 803 are connected togetherthrough straight wires 805 and a split side ring 503, similar to thatdescribed above in connection with FIGS. 5 and 6.

In yet another embodiment, a simple filter is shown in FIGS. 10 and 11in side and top view, respectively. This filter 1001 also has a centralechogenic tube 301, supporting a plurality of wire legs 1003. Wire legs1003 each have a radially extending portion 1005, arranged to form afilter cone, and a longitudinally extending portion 1007. Thelongitudinally extending portion 1007 centers and axially aligns thefilter with the axis of the vessel in which it is to be implanted,similar to the action of centering loops 305 and the middle strand 105of the above described embodiments. The longitudinally extendingportions 1007 end in loops 1009 and points 1011, which securely anchorthe filter in the vessel in which it is implanted.

Although the members of the filters arranged to trap blood clotsdescribed above all are wires, aspects of the invention can be embodiedin slotted tube filter designs, now described in connection with FIGS.12-18. Three designs are shown and described, along with somevariations. The three designs are a twisted, slotted tube, a conicslotted tube and a simple expanded slotted tube.

Each of these designs is preferably constructed of a biologicallytolerated temperature-sensitive shape memory material such as nitinol.Any of the designs constructed using nitinol are bent into their final,deployed shape in a sodium iodide bath at human body temperature. Whenthe filter is returned to room ambient temperature, or anothertemperature not human body temperature, the nitinol members relax backinto their unbent shapes, generally a compact shape suitable formovement through the patient's blood vessels to the desired location.

The twisted slotted tube is now described in connection with FIGS.12-15.

When expanded into deployed configuration, the twisted slotted tubefilter 1200 has the shape shown in FIG. 12. Members 1201, formed of thematerial of a tube between slots in region 1202, connect to tubes 1203,1204, which remain outside of region 1202. Members 1201 trace part of ahelix from one tube 1203 to the other 1204 (see also FIG. 14). Theconfiguration of FIG. 12 can be manufactured from a simple slotted tubeas shown in FIG. 13. As shown in FIG. 13, slots divide the entire region1202 into members 1201, as previously described. Members 1201 areexpanded outward as tube 1204 is rotated about 180° relative to tube1203, resulting in the FIG. 12 configuration (note positions of pointsA, B, A′, B′). As seen in the top view of FIG. 15, members 1201 blockclots of a substantial size, while allowing substantial normal bloodflow.

In order to increase sonographic conspicuousness of filter 1200, one ormore regions 1205, 1206, 1207 can be textured, for example by stampingor etching. A high degree of sonoconspicuousness in regions 1205, 1207is advantageous in that the extent of the filter is bracketed thereby.Highlighting region 1206 is advantageous in pointing out the center ofthe filter placement. Regions 1205, 1206, 1207 can be renderedsonoconspicuous by other known means, also, such as by applying suitablecoatings or any of the other means discussed above. Othersonoconspicuous regions can also be used as may be consideredadvantageous, even rendering the entire filter surface sonoconspicuousby texturing, coating, etc.

The conic slotted tube filter is now described in connection with FIGS.16 and 17.

The filter 1600 has members 1601 attached at one end to a tube 1602, asshown in FIG. 16. This configuration is easily achieved from thestarting point shown in FIG. 17. A tube 1700 is slotted in region 1701,leaving solid tube 1602. The resulting members are folded back to formthe configuration of FIG. 16. Texture or other sonographic highlightingcan be applied to regions 1603, 1604, or any other region consideredadvantageous, as described above in connection with the twisted slottedtube filter.

Finally, a simple slotted tube filter is described in connection withFIG. 18.

The filter 1800 of FIG. 18 is similar to that of FIGS. 12-15. However,members 1801 of filter 1800 are not twisted as members 1201 of filter1200 are. Otherwise, filter 1800 has tubes 1203, 1204 andsonoconspicuous regions 1205, 1206, 1207 or elsewhere as consideredadvantageous, also as described above.

Filters embodying aspects of the invention are generally used in thesame manner as other filters used in this art. However, the imaging usedin connection with embodiments of the invention can be sonographic,rather than fluoroscopic. A combination of sonography and fluoroscopycan also be used in connection with embodiments of the invention.

Filters are generally delivered in a compact configuration and expandedeither mechanically or by temperature sensitive shape memory effects toa deployed configuration when they reach the placement location.

The invention can be embodied in a complete set using any of theabove-described filters or variations. The set employs a #7 or #8 Frenchdilator having an echogenic tip. The set further includes a #8 Frenchsheath, also having an echogenic tip, of flexible plastic. Finally, theset is guided by a 0.035 inch (0.89 mm) diameter guide or marker wirehaving one or more, preferably three, echogenic sites at or near thedistal end thereof. The guide or marker wire may be a straight wire or acurved wire, as described below in connection with FIGS. 19-21. The setthus described can be used to implant a filter using only externalsonography or a combination of external sonography with othertechniques, as described below. Although components of the set may beseparately available, it is expect that the dilator, sheath, guide wireend filter will be supplied as a complete set also, for convenience andconsistency.

Delivery and deployment of a filter, e.g., FIG. 1, 101, having anechogenic lead 123, below the renal vein proceeds as follows. Otherfilters are delivered and deployed similarly.

The locations of the renal veins are determined and marked on the skinwith marker, using any conventional means. This may include thetechniques for internal sonography described by Bonn et al.,Intravascular Ultrasound as an Alternative to Positive-contrast VenaCavography prior to Filter Placement, Journal of Vascular InterventionalRadiology, Vol. 10, No. 7, pp. 843-849, 1999. Alternatively, externalsonography can also be used to locate the renal veins.

As shown in FIGS. 19-21, a curved guide wire 1901 having a series ofsonographically conspicuous features 1903, for example 3-12 featuresspaced about 1 cm apart, is then inserted to a point just past theconfluence 1905 of the renal veins 1907 forming the vena cava 1909, andthen withdrawn to engage one renal vein 1907. Once the wire 1901 engagesthe renal vein 1907, slight advancement anchors the renal vein 1907. Theprogress of the curved, sonographically conspicuous wire 1901 is easilyfollowed using external sonography.

The guide wire, particularly the curved guide wire 1901 introduced asdescribed above, and the echogenic features of the guide wire makepossible very precise identification using external sonography of thedesired placement location. The dilator is then introduced over theguide wire and the echogenic tip thereof is also followed by externalsonography to the filter placement location. Finally, the filter,contained in the end of the sheath, is guided over the guide wire,inside of the dilator, to the placement location and deployed. Theprecise location of the filter is followed using external sonography.

The filters described above are very flexible, having low profiles,i.e., small undeployed diameters and short lengths, permitting access tothe patient's venous system through various conventional locations,including the jugular vein, the groin vein, etc. Moreover, because thefilter features avoid foreshortening of the filter relative to thedistal end thereof, highly accurate tracking and placement is achievedby simply visualizing the distal end of the filter as it progresses tothe placement location.

In addition to the sonographically conspicuous features described above,other features can provide sonographic conspicuousness. For example,textured surfaces and sharp edges and other geometries known to besonographically conspicuous can be used. Such alternativesonographically conspicuous features are readily provided in so-calledslotted tube filter constructions, now described.

Delivery and deployment of a filter below the renal veins with anechogenic tube 301 instead of or in addition to an echogenic lead 123proceeds in similar fashion, but with some advantages now described inconnection with FIGS. 22-24. Principally, when using a filter configuredwith an echogenic tube 301, or other configuration of sonographicallyconspicuous features which are aligned to show the axial alignment andposition of the filter, the filter can be slid over a marker wire 2201,as generally shown in FIG. 22 while the true longitudinal position andaxial orientation of the filter is correctly visualized.

As shown in the sonographic image sketched in FIG. 23, when thesonographic beam is aligned with the tube 301 and the marker wire 2201,a true image 2301 is obtained, and the true longitudinal and axialposition can be determined from the angle of incidence of the beam andthe depth of the tube 301 and wire 2201 within the true image 2301. Thetrue image 2301 of FIG. 23 is contrasted with the oblique image 2401 ofFIG. 24, in which incomplete information is available. In this obliqueimage 2401, the angle of incidence of the beam is turned slightly, sothat only a portion of tube 301 and marker wire 2201 are each visible inthe oblique image 2401. When such an oblique image 2401 presents itself,the surgeon guiding the filter including tube 301 can determine whetherthe visible portion of tube 301 represents the distal or proximal end ofthe filter and either guide the filter accordingly or adjust thesonogram beam or the filter position to obtain a true image 2301.

It is expected that struts, and other filter parts which do notspecifically include sonographically conspicuous features will bedifficult or impossible to see, while the tube 301 will be easily seen.Thus, the tube 301 and marker wire 2201 combine in the image to permitoptimum sonographic imaging to be arranged.

The overall filter and placement set and procedures described abovepermit filter placement by a physician at bedside, in an office (ascompared to hospital) setting, or in a sonographic suite. Thus, the needfor a fluoroscopic suite or equipment is obviated by the inventivefilters, placement sets and methods. The inventive filters, placementsets and methods are also appropriate for intraoperative placement wherefluoroscopy is not available, cumbersome, inappropriate or otherwiseuntenable due to operating room facilities, availability, and requiredprocedures or contraindication of any other kind.

When desired, the filters and methods of the present invention can beassisted by magneto-resonant (MR) and computed tomography (CT)visualization methods. Such methods are particularly suitable when thefilter is constructed of nitinol or another material, which shows up inan MR or CT image. Fluoroscopic assistance can also be used with nitinolfilter structures, as well as other materials that show up in afluoroscopic image. A highly visible marker wire may also be helpful tothese methods.

The invention has now been shown and described in connection with anembodiment thereof and some variations, but the invention is not limitedthereto. Other variations should now be evident to those skilled in thisart, and are contemplated as falling within the scope of the inventionwhich is limited only by the following claims and equivalents thereto.

What is claimed is:
 1. A filter, implantable in a blood vessel bysonographic visualization, comprising: one or more members arranged totrap blood clots without substantially interfering with normal bloodflow; and a sonographically conspicuous feature on at least one member,so the filter position can be determined by sonographic visualization.2. The filter of claim 1, wherein the sonographically conspicuousfeature is an echogenic feature.
 3. The filter of claim 2, wherein theechogenic feature comprises: a textured surface.
 4. The filter of claim3, wherein the textured surface comprises: an etched region.
 5. Thefilter of claim 2, wherein the echogenic feature comprises: at least oneof a sharp corner and a sharp edge.
 6. The filter of claim 2, whereinthe echogenic feature comprises: an echogenic coating.
 7. The filter ofclaim 2, wherein a marker wire is employed to assist in placement, themarker wire further comprising: a plurality of echogenic markers on themarker wire, whereby correct visualization in a sonogram of a truelongitudinal slice along the filter axis is readily ascertainable bypresence in the sonogram of each of the plurality of echogenic markers.8. The filter of claim 7, wherein the filter further comprises: a tubethrough which the marker wire is threaded, correct visualizationadditionally confirmed by presence in the sonogram of the tube in itsentirety.
 9. The filter of claim 2, wherein correct visualization in asonogram of a true longitudinal slice along the filter axis is readilyascertainable by presence in the sonogram of the echogenic feature. 10.The filter of claim 9, wherein the filter further comprises: anadditional echogenic feature, correct visualization additionallyconfirmed by presence in the sonogram of both the echogenic feature andthe additional echogenic feature.
 11. The filter of claim 2, wherein theone or more members are arranged to define a cone-shaped basket attachedto the echogenic feature at a vertex.
 12. The filter of claim 11,wherein the members are further arranged to define a substantiallycoplanar flower, the echogenic feature attached thereto at a centerthereof.
 13. The filter of claim 12, further comprising an outer ringconnecting a base of the cone to an outer position of the flower. 14.The filter of claim 11, further comprising: a plurality of echogenicmarkers substantially at a periphery of a base of the cone.
 15. Thefilter of claim 11, further comprising: a plurality of loops at aperiphery of the basket, whereby the basket is axially aligned therebyduring deployment thereof.
 16. The filter of claim 11, wherein thebasket is defined by substantially radially extending members.
 17. Thefilter of claim 11, wherein the basket is defined by a mesh of membersextending in both radial directions and directions transverse the radialdirections.
 18. The filter of claim 2, further comprising: a pluralityof echogenic markers substantially at a periphery of the filter, wherebydeployment thereof can be visualized.
 19. The filter of claim 2, furthercomprising: an expanded, slotted tube having slots along a predeterminedlength thereof, the slots dividing the slotted tube into the one or moremembers.
 20. The filter of claim 2 wherein the one or more members arecomposed of a material having a temperature-sensitive shape memory. 21.The filter of claim 20 wherein the filter has a deployed shape at humanbody temperature and a compact shape for implantation at a temperatureother than human body temperature.
 22. The filter of claim 1, whereinthe sonographically conspicuous feature is a sonically absorptivefeature.
 23. The filter of claim 22, wherein the sonically absorptivefeature is a coating.
 24. A caval filter placement set, comprising: aguide wire; a dilator; a sheath for introducing the filter; and a cavalfilter including one or more members arranged to trap blood clotswithout substantially interfering with normal blood flow; and asonographically conspicuous feature on the caval filter, so the filterposition can be determined by sonographic visualization.
 25. The set ofclaim 24, wherein the sonographically conspicuous feature is anechogenic feature.
 26. The set of claim 25, the sheath furthercomprising an echogenic feature at a distal end thereof.
 27. The set ofclaim 25, the dilator further comprising an echogenic feature at adistal end thereof.
 28. The set of claim 25, the guide wire furthercomprising plural echogenic features.
 29. The set of claim 28, whereinthe guide wire has a hooked end, which can engage a renal vein whenpositioned in the cava.
 30. The filter of claim 24, wherein thesonographically conspicuous feature is a sonically absorptive feature.31. The filter of claim 30, wherein the sonically absorptive feature isa coating.